1. Field of the Invention
The present invention relates to a relay type zoom viewfinder system for a single reflex camera capable of trimming or panoramic photographing.
2. Description of the Prior Art
Recently, a trimming system applied to a camera is provided. In this system, a predetermined area A of an image forming area B of a film 141 shown in FIG. 14(A), for example, can be enlarged in printing to an area A' of a photographic paper 143 shown in FIG. 14(B) by recording information of the area A on a predetermined place 142 of an emulsion surface of the film 141.
That is to say, in a trimming mode, trimming information is recorded on the predetermined place 142 of the film 141, and a reading device reads the information in printing. Then, in accordance with the information, a printing system enlarges the area A by zooming.
The zooming operation performed according to the trimming information is called "electronic zooming (EZ)" or "pseudo zooming". A ratio of the length of a diagonal of an area determined according to the EZ to the length of a diagonal of a film is called a trimming magnification.
A panoramic photographing system is also provided as well the trimming system. In the trimming system, a photographing area is enlarged at the same aspect ratio as in a regular system. However, in the panoramic photographing system, the aspect ratio is not same. Namely, in the panoramic photographing system, a photographing area C does not include the upper and lower parts of the film as shown in FIG. 14(A), so that a printed picture is more oblong than in the regular system when the photographing area C is enlarged. Panoramic photographing information is recorded on the predetermined place 142 of the film as well as the above described trimming information.
As a TTL viewfinder system which can be applied to the trimming system, one observed through an eyepiece optical system and a relay zoom optical system is considered. In the TTL viewfinder system like this, a frame limit member does not need to be moved in accordance with a pseudo zooming operation, and the zooming ratio can be easily high. These are merits of the above mentioned TTL viewfinder system. However, in order to obtain a good finder image in the relay zoom optical system, the length from a first image plane to a second image plane has to be long. When the length is long, a viewfinder becomes big.
A viewfinder system which is made as small as possible as a whole by refracting a light bundle from the first image plane to the second image plane with mirrors is conventionally known. (Japanese Laid-Open Patent Applications No. Sho 64-68739, No. Hei 1-103071, No. Hei 1-231013, No. Hei 2-120833 and No. Hei 2-120834 and Japanese Laid-Open Utility Model No. Hei 2-3530)
Nevertheless, though a light bundle from the first image plane to the second image plane is refracted by mirrors, the length of an optical path of a relay zoom optical system is long. Therefore, plural reflecting members such as a mirror is needed so as to make a viewfinder system small. The more the reflecting members are used, the more the manufacturing process becomes complicated. Then, the optical axis is deviated. It causes a problem that a range observed through a viewfinder system is out of a photographing range.
As a zoom viewfinder system for a common single reflex camera, which can be applied to the trimming system, one in which a relay zoom optical system and an eyepiece optical system are fixed in a holder and a zooming operation is carried out by shifting a part of the relay zoom optical system is considered.
However, in this structure, reflecting members for reflecting a light path must be fixed in the holder with the relay zoom optical system so that the viewfinder system should be applied to a single reflex camera. The purpose of reflecting the light path with the reflecting members is to prevent the camera body from being big by making the finder optical system as small as possible. Then, the above structure has problems.
For example, the complicated structure of the holder makes the manufacture of the holder difficult. Moreover, when the structure of the holder becomes complicated, it becomes harder to fix the relay zoom optical system and the reflecting members to the holder, and that causes the difficulty of keeping the zooming precision high. Thus, in the above described structure, not only manufacturing and maintaining the viewfinder system are difficult, but also the zooming precision is low.
In addition, when a part of the relay zoom optical system are shifted by a driving system for a zooming operation, unnecessary power is transmitted to all parts of the holder directly, and as a result, a distortion of the holder occurs, and the optical axis is shifted.
The length of an optical path of a viewfinder system including a relay zoom optical system is longer than that of a viewfinder system using a penta-prism, so that reflecting members are provided in the relay type zoom viewfinder system in order to make the viewfinder system small. For example, a relay type zoom viewfinder system using Porro-mirrors as reflecting members is known. In this viewfinder system, a Porro-mirror is composed of two flat mirrors held in one with a holding member so that an angle between the two mirrors should be 90.degree..
A reflecting member such as a Porro-mirror, whose two reflecting surfaces are formed with a mold of glass or plastic, can be formed with high precision in relative positions of the two reflecting surfaces. However, different from the case of a pentaprism, in the case of such a reflecting member, convergent rays do not pass through a medium such as glass and plastic provided between two parallel reflecting surfaces. Therefore, the optical light path becomes long, so that a viewfinder system becomes big in size. Thus, the reflecting member such as a Porro-mirror is not suitable for a viewfinder which uses an optical system such as a relay optical system, that is, a viewfinder where an extremely long light path must be included. Furthermore, even if the relative positions of the two reflecting members can be determined precisely, an error of the fitting positions of the reflecting members owing to an error in fitting holding members and such causes a deviation of the light axis. As a result, an area observed through a viewfinder system does not correspond with an area to be photographed practically.